It is known that amorphous synthetic silicas may be used as cleansing agents in toothpastes. Silicas, used as cleansing agents, have the vital advantage over the previously used calcium phosphates and chalks that they do not react with the fluoride ions frequently employed in the form of tin(II) fluoride and sodium fluoride as anti-caries agents, and thus do not block the effect of these additives.
Accordingly, there is no need to replace the cleansing agents based on calcium phosphates and chalks by an inert substance.
A first vital successful step in this direction was the introduction of amorphous highly porous silica xerogels (U.S. Pat. No. 3,538,230), the combination of which with thickening aerogels, for example Syloid 244.RTM., finally allowed the commercial breakthrough of the use of silica gels in toothpastes. However, it must be pointed out that use had been made much earlier of the viscosity-regulating effect of certain silicas, for example pyrogenic and precipitated silicas having a high degree of structure (German Pat. No. 1,667,875) corresponding to U.S. Pat. No. 3,705,940 and British Pat. No. 1,241,877. In subsequent development, the combination of cleansing agents based on silica xerogels with pyrogenic silicas (German Published Application DAS No. 2,033,678) corresponding to U.S. Pat. No. 3,689,637 and British Pat. No. 1,298,130 and with thickening precipitated silicas having a medium to high degree of structure (British Pat. No. 1,433,743, German Published Application DAS No. 2,610,207 and U.S. Pat. No. 4,132,806) was, logically, also pursued.
The next step with regard to the production of improved novel cleansing agents was the development of a specific aluminum silicate produced by precipitation, and the combination of this silicate with a thickening pyrogenic silica or with a thickening precipitated silica of medium to high degree of structure is described in German Pat. No. 2,154,376 corresponding to British Pat. No 1,400,793 and German Published Application DAS No. 2,206,285 corresponding to British Pat. No. 1.372,663.
Subsequent development next led to cleansing agents based on precipitated silicas which produced no significant thickening action but had markedly lower abrasiveness than the calcium phosphate cleansing agents. Where these novel SiO.sub.2 -based precipitated silicas are used, the rheology of the toothpastes is not regulated by means of thickening precipitated silicas, but by addition of special binders such as seaweed colloids or synthetic cellulose derivatives (carragheen and sodium carboxymethylcellulose) and by means of vegetable gums (German Laid-Open Application DOS No. 2,344,316; U.S. Pat. No. 4,105,757; German Laid-Open Application DOS No. 2,344,805; U.S. Pat. Nos. 4,122,160 and 4,144,321, and German Laid-Open Application DOS No. 2,522,486) corresponding to U.S. Pat. Nos. 4,067,746 and 4,191,742.
Nowadays, a modern cleansing agent based on silicas and intended for use in toothpastes has to provide the following effects:
reduced abrasiveness, in the sense of medium polishing activity (Cu abrasion in the finished toothpaste, between 8 and 14 mg), in order to protect the dental enamel,
at filler contents in the range of 15-25% by weight, based on the amount of one and the same bifunctional cleansing agent (producing both abrasion and thickening), the viscosity, under conditions which give the above Cu abrasion range, should be between 2,500 and 4,500 mPa.s (determined by the Rotovisko-PK method),
the ribbon of toothpaste leaving the tube should be smooth, glossy and free from specks and
the dental-care composition containing the cleansing agent should have improved shelf life, in the sense of exhibiting constant abrasiveness and degree of thickening (no after-thickening) for a period of at least one year.
It is an object of the invention to conform to the above requirements of a dental-care composition by choice and use of a suitable cleansing agent.